调用中缺少参数“completionHandler”的参数答案

【问题标题】：Missing argument for parameter 'completionHandler' in call调用中缺少参数“completionHandler”的参数
【发布时间】：2015-07-23 14:34:34
【问题描述】：

我使用了在 swift 1.0 中工作的函数 geocodeAddressString，但在 swift2 中没有。谁能告诉我我的代码有什么问题以及如何解决这个问题？谢谢！

geocoder.geocodeAddressString(address, {(placemarks: [AnyObject], error: NSError) -> Void in  //Error: Missing argument for parameter 'completionHandler' in call

        if let placemark = placemarks?[0] as? CLPlacemark {
            let annotation = MKPointAnnotation()
            let location:CLLocationCoordinate2D = CLLocationCoordinate2DMake(placemark.location.coordinate.latitude, placemark.location.coordinate.longitude)
            annotation.coordinate = location
            annotation.title = "\(StudentArray[student].firstName), \(StudentArray[student].lastName)"
            annotation.subtitle = "\(StudentArray[student].grade)"
            self.mapView.addAnnotation(annotation)
        }

    })

【问题讨论】：

标签： swift completionhandler completion

【解决方案1】：

要么指定completionHandler参数名称：

geocoder.geocodeAddressString(address, completionHandler: { placemarks, error in
    if let placemark = placemarks.first as? CLPlacemark {
        let annotation = MKPointAnnotation()
        let location = CLLocationCoordinate2DMake(placemark.location.coordinate.latitude, placemark.location.coordinate.longitude)
        annotation.coordinate = location
        annotation.title = "\(StudentArray[student].firstName), \(StudentArray[student].lastName)"
        annotation.subtitle = "\(StudentArray[student].grade)"
        self.mapView.addAnnotation(annotation)
    }
})

或使用尾随闭包语法（参见 Trailing Closure 部分 ClosuresSwift 编程语言章节），您可以从 @987654324 中拉出闭包@和)放在)之后：

geocoder.geocodeAddressString(address) { placemarks, error in
    if let placemark = placemarks.first as? CLPlacemark {
        let annotation = MKPointAnnotation()
        let location = CLLocationCoordinate2DMake(placemark.location.coordinate.latitude, placemark.location.coordinate.longitude)
        annotation.coordinate = location
        annotation.title = "\(StudentArray[student].firstName), \(StudentArray[student].lastName)"
        annotation.subtitle = "\(StudentArray[student].grade)"
        self.mapView.addAnnotation(annotation)
    }
}

【讨论】：

感谢您提供此示例！尾随闭包语法总是让我感到困惑，因为它省略了部分参数，但现在我发现它只是简单的练习。

【解决方案2】：

在完成处理程序之前添加参数。

geocoder.geocodeAddressString(address, completionHandler: {(placemarks: [AnyObject], error: NSError) -> Void in  // Added argument for parameter 'completionHandler' in call

    if let placemark = placemarks?[0] as? CLPlacemark {
        let annotation = MKPointAnnotation()
        let location:CLLocationCoordinate2D = CLLocationCoordinate2DMake(placemark.location.coordinate.latitude, placemark.location.coordinate.longitude)
        annotation.coordinate = location
        annotation.title = "\(StudentArray[student].firstName), \(StudentArray[student].lastName)"
        annotation.subtitle = "\(StudentArray[student].grade)"
        self.mapView.addAnnotation(annotation)
    }

})

【讨论】：